webwork中的这一个类有什么作用？

Question

webwork中的这一个类有什么作用？
解释一下代码

/*

• Copyright (c) 2002-2003 by OpenSymphony
• All rights reserved. */ package com.opensymphony.webwork.components;

import com.opensymphony.webwork.util.FastByteArrayOutputStream;
import com.opensymphony.webwork.views.jsp.TagUtils;
import com.opensymphony.webwork.views.util.ContextUtil;
import com.opensymphony.webwork.views.util.UrlHelper;
import com.opensymphony.webwork.dispatcher.mapper.ActionMapping;
import com.opensymphony.webwork.dispatcher.mapper.ActionMapper;
import com.opensymphony.webwork.dispatcher.mapper.ActionMapperFactory;
import com.opensymphony.webwork.WebWorkException;
import com.opensymphony.xwork.util.OgnlValueStack;
import com.opensymphony.xwork.util.TextParseUtil;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.Writer;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Stack;

/**

• Base class to extend for UI components.
• This class is a good extension point when building reuseable UI components. *
• @author plightbo
• @author tm_jee

• @version $Date: 2007-02-16 08:15:36 +0100 (Fri, 16 Feb 2007) $ $Id: Component.java 2846 2007-02-16 07:15:36Z tm_jee $
  */
  public class Component {
  private static final Log LOG = LogFactory.getLog(Component.class);

  public static final String COMPONENT_STACK = "__component_stack";

  protected OgnlValueStack stack;
  protected Map parameters;
  protected String id;

  /**

  • Constructor. *
  • @param stack OGNL value stack. */ public Component(OgnlValueStack stack) { this.stack = stack; this.parameters = new HashMap(); getComponentStack().push(this); }

  /**

  • Get's the name of this component.

  • @return the name of this component.
    */
    private String getComponentName() {
    Class c = getClass();
    String name = c.getName();
    int dot = name.lastIndexOf('.');

    return name.substring(dot + 1).toLowerCase();
    }

  /**

  • Get's the OGNL value stack assoicated with this component.
  • @return the OGNL value stack assoicated with this component. */ public OgnlValueStack getStack() { return stack; }

  /**

  • Get's the component stack of this component.
  • @return the component stack of this component, never null. */ public Stack getComponentStack() { Stack componentStack = (Stack) stack.getContext().get(COMPONENT_STACK); if (componentStack == null) { componentStack = new Stack(); stack.getContext().put(COMPONENT_STACK, componentStack); } return componentStack; }

  /**

  • Callback for the start tag of this component.
  • Should the body be evaluated? *
  • @param writer the output writer.
  • @return true if the body should be evaluated */ public boolean start(Writer writer) { return true; }

  /**

  • Callback for the end tag of this component.
  • Should the body be evaluated again?
  • NOTE: will pop component stack.
  • @param writer the output writer.
  • @param body the rendered body.
  • @return true if the body should be evaluated again */ public boolean end(Writer writer, String body) { return end(writer, body, true); }

  /**

  • Callback for the start tag of this component.
  • Should the body be evaluated again?
  • NOTE: has a parameter to determine to pop the component stack.
  • @param writer the output writer.
  • @param body the rendered body.
  • @param popComponentStack should the component stack be popped?

  • @return true if the body should be evaluated again
    */
    protected boolean end(Writer writer, String body, boolean popComponentStack) {
    assert(body != null);

    try {
    writer.write(body);
    } catch (IOException e) {
    throw new WebWorkException("IOError while writing the body: " + e.getMessage(), e);
    }
    if (popComponentStack) {
    popComponentStack();
    }
    return false;
    }

  /**

  • Pops the component stack. */ protected void popComponentStack() { getComponentStack().pop(); }

  /**

  • Finds the nearest ancestor of this component stack.
  • @param clazz the class to look for, or if assignable from.

  • @return the component if found, null if not.
    */
    protected Component findAncestor(Class clazz) {
    Stack componentStack = getComponentStack();
    int currPosition = componentStack.search(this);
    if (currPosition >= 0) {
    int start = componentStack.size() - currPosition - 1;

    //for (int i = componentStack.size() - 2; i >= 0; i--) {
    for (int i = start; i >=0; i--) {
        Component component = (Component) componentStack.get(i);
        if (clazz.isAssignableFrom(component.getClass()) && component != this) {
            return component;
        }
    }
    

    }

    return null;
    }

  /**

  • Evaluates the OGNL stack to find a String value.
  • @param expr OGNL expression.
  • @return the String value found. */ protected String findString(String expr) { return (String) findValue(expr, String.class); }

  /**

  • Evaluates the OGNL stack to find a String value.
  • If the given expression is null a error is logged and a WebWorkException is thrown
  • constructed with a messaged based on the given field and errorMsg paramter. *
  • @param expr OGNL expression.
  • @param field field name used when throwing WebWorkException.
  • @param errorMsg error message used when throwing WebWorkException.
  • @return the String value found.
  • @throws WebWorkException is thrown in case of expression is null. */ protected String findString(String expr, String field, String errorMsg) { if (expr == null) { throw fieldError(field, errorMsg, null); } else { return findString(expr); } }

  /**

  • Constructs?a WebWorkException based on the given information.
  • A message is constructed and logged at ERROR level before being returned
  • as a WebWorkException.
  • @param field field name used when throwing WebWorkException.
  • @param errorMsg error message used when throwing WebWorkException.
  • @param e the caused exception, can be null.
  • @return the constructed WebWorkException. */ protected WebWorkException fieldError(String field, String errorMsg, Exception e) { String msg = "tag '" + getComponentName() + "', field '" + field + ( id != null ?"', id '" + id:"") + ( parameters != null && parameters.containsKey("name")?"', name '" + parameters.get("name"):"") + "': " + errorMsg; if (e == null) { LOG.error(msg); return new WebWorkException(msg); } else { LOG.error(msg, e); return new WebWorkException(msg, e); } }

  /**

  • Finds a value from the OGNL stack based on the given expression.
  • @param expr the expression. Returns null if expr is null.

  • @return the value, null if not found.
    */
    protected Object findValue(String expr) {
    if (expr == null) {
    return null;
    }

    if (altSyntax()) {
    // does the expression start with %{ and end with }? if so, just cut it off!
    if (expr.startsWith("%{") && expr.endsWith("}")) {
    expr = expr.substring(2, expr.length() - 1);
    }
    }

    return getStack().findValue(expr);
    }

  /**

  • Is the altSyntax enabled?
  • See webwork.properties where the altSyntax flag is defined.
  • Note: Since WebWork 2.17 the altSyntax is default true.
  • @return true if the altSyntax is enabled. */ public boolean altSyntax() { return ContextUtil.isUseAltSyntax(stack.getContext()); }

  /**

  • Evaluates the OGNL stack to find an Object value.
  • If the given expression is null a error is logged and a WebWorkException is thrown
  • constructed with a messaged based on the given field and errorMsg paramter. *
  • @param expr OGNL expression.
  • @param field field name used when throwing WebWorkException.
  • @param errorMsg error message used when throwing WebWorkException.
  • @return the Object found, is never null.

  • @throws WebWorkException is thrown in case of not found in the OGNL stack, or expression is null.
    */
    protected Object findValue(String expr, String field, String errorMsg) {
    if (expr == null) {
    throw fieldError(field, errorMsg, null);
    } else {
    Object value = null;
    Exception problem = null;
    try {
    value = findValue(expr);
    } catch (Exception e) {
    problem = e;
    }

    if (value == null) {
        throw fieldError(field, errorMsg, problem);
    }
    
    return value;
    

    }
    }

  /**

  • Evaluates the OGNL stack to find an Object of the given type.
  • This method only supports the altSyntax. So this should be set to true.
  • @param expr OGNL expression.
  • @param toType the type expected to find.

  • @return the Object found, or null if not found.
    */
    protected Object findValue(String expr, Class toType) {
    if (altSyntax() && toType == String.class) {
    return TextParseUtil.translateVariables('%', expr, stack);
    } else {
    if (altSyntax()) {
    // does the expression start with %{ and end with }? if so, just cut it off!
    if (expr.startsWith("%{") && expr.endsWith("}")) {
    expr = expr.substring(2, expr.length() - 1);
    }
    }

    return getStack().findValue(expr, toType);
    

    }
    }

  /**

  • Renders an action URL by consulting the {@link com.opensymphony.webwork.dispatcher.mapper.ActionMapper}.
  • @param action the action
  • @param namespace the namespace
  • @param method the method
  • @param req HTTP request
  • @param res HTTP response
  • @param parameters parameters
  • @param scheme http or https
  • @param includeContext should the context path be included or not
  • @param encodeResult should the url be encoded
  • @return the action url. */ protected String determineActionURL(String action, String namespace, String method, HttpServletRequest req, HttpServletResponse res, Map parameters, String scheme, boolean includeContext, boolean encodeResult, boolean escapeXml) { String finalAction = findString(action); String finalNamespace = determineNamespace(namespace, getStack(), req); ActionMapping mapping = new ActionMapping(finalAction, finalNamespace, method, parameters); ActionMapper mapper = ActionMapperFactory.getMapper(); String uri = mapper.getUriFromActionMapping(mapping); return UrlHelper.buildUrl(uri, req, res, parameters, scheme, includeContext, encodeResult, false, escapeXml); }

  /**

  • Determines the namespace of the current page being renderdd. Useful for Form, URL, and href generations.
  • @param namespace the namespace
  • @param stack OGNL value stack
  • @param req HTTP request

  • @return the namepsace of the current page being rendered, is never null.
    */
    protected String determineNamespace(String namespace, OgnlValueStack stack, HttpServletRequest req) {
    String result;

    if (namespace == null) {
    result = TagUtils.buildNamespace(stack, req);
    } else {
    result = findString(namespace);
    }

    if (result == null) {
    result = "";
    }

    return result;
    }

  /**

  • Pushes this component's parameter Map as well as the component itself on to the stack
  • and then copies the supplied parameters over. Because the component's parameter Map is
  • pushed before the component itself, any key-value pair that can't be assigned to componet
  • will be set in the parameters Map. *
  • @param params the parameters to copy. */ public void copyParams(Map params) { stack.push(parameters); stack.push(this); try { for (Iterator iterator = params.entrySet().iterator(); iterator.hasNext();) { Map.Entry entry = (Map.Entry) iterator.next(); String key = (String) entry.getKey(); stack.setValue(key, entry.getValue()); } } finally { stack.pop(); stack.pop(); } }

  /**

  • Constructs a string representation of the given exception.
  • @param t the exception

  • @return the exception as a string.
    */
    protected String toString(Throwable t) {
    FastByteArrayOutputStream bout = new FastByteArrayOutputStream();
    PrintWriter wrt = new PrintWriter(bout);
    t.printStackTrace(wrt);
    wrt.close();

    return bout.toString();
    }

  /**

  • Get's the parameters.
  • @return the parameters. Is never null. */ public Map getParameters() { return parameters; }

  /**

  • Add's all the given parameters to this componenets own parameters.
  • @param params the parameters to add. */ public void addAllParameters(Map params) { parameters.putAll(params); }

  /**

  • Add's the given key and value to this components own parameter.
  • If the provided key is null nothing happends.
  • If the provided value is null any existing parameter with
  • the given key name is removed.
  • @param key the key of the new parameter to add.

  • @param value the value assoicated with the key.
    */
    public void addParameter(String key, Object value) {
    if (key != null) {
    Map params = getParameters();

    if (value == null) {
        params.remove(key);
    } else {
        params.put(key, value);
    }
    

    }
    }

  /**

  • Get's the id for referencing element.
  • @return the id for referencing element. */ public String getId() { return id; }

  /**

  • id for referencing element. For UI and form tags it will be used as HTML id attribute
  • @ww.tagattribute required="false" */ public void setId(String id) { if (id != null) { this.id = findString(id); } }

  /**

  • Overwrite to set if body shold be used.
  • @return always false for this component. */ public boolean usesBody() { return false; }

}

Answer 1

webwork标签实体基类，所有的标签实体都继承这个类，在具体标签的tag类中实例化实体，你如果要自定义标签，也可以继承这个类，可以看看相关webwork标签的资料。